(May 13, 2010) — A major survey of lizard populations worldwide has found an alarming pattern of population extinctions attributable to rising temperatures. If current trends continue, 20 percent of all lizard species could go extinct by 2080, according to an international research team that includes biologists at University of California, Santa Cruz, and Ohio University.

“It’s a wake-up call that we’re looking at a potential ecological catastrophe. We’re likely to see extinctions in our backyard,” said Don Miles, a professor of biological sciences at Ohio University involved in the research.

Research on spiny lizards in Mexico, such as this Sceloporus mucronatus, revealed a pattern of local population extinctions and enabled investigators to develop a global model of extinction risk.Photo by Fausto Mendez-de la Cruz.

In the study, led by University of California at Santa Cruz scientist Barry Sinervo and published in the May 14 issue of Science, the researchers surveyed lizard populations, studied the effects of rising temperatures on lizards, and used their findings to develop a predictive model of extinction risk. Their model accurately predicted specific locations on five continents (North and South America, Europe, Africa and Australia) where previously studied lizard populations have already gone locally extinct.

“We did a lot of work on the ground to validate the model and show that the extinctions are the result of climate change,” said Sinervo, a professor of ecology and evolutionary biology. “None of these are due to habitat loss. These sites are not disturbed in any way, and most of them are in national parks or other protected areas. Our research shows that the ongoing extinctions of lizards are directly due to climate warming from 1975 to the present.”

The disappearance of lizard populations is likely to have repercussions across the food chain. Lizards are important prey for many birds, snakes and other animals, and are important predators of insects.

Sinervo and Miles spotted signs of trouble when they found that lizard populations other researchers had studied in the 1980s and 1990s had disappeared. This happened first in France, where they worked with French researchers Benoit Heulin and Jean Clobert, and later in Mexico, where they worked with Jack Sites of Brigham Young University and Mexican herpetologist Fausto Méndez de la Cruz. In Mexico, Sinervo, Miles and Méndez de la Cruz and their students resurveyed 48 species of spiny lizards (Sceloporus) at 200 sites where the lizards had been studied between 1975 and 1995. They found that 12 percent of the local populations had gone extinct.

To investigate the link between these extinctions and temperature, the team built a device that would mimic the body temperature of a lizard basking in the sun and record the temperatures on a microchip. They set the devices in sun-exposed sites for four months in locations with and without surviving populations of blue spiny lizards.

“The results were clear,” Sinervo said. “These lizards need to bask in the sun to warm up, but if it gets too hot they have to retreat into the shade, and then they can’t hunt for food. At the extinct sites in the Yucatan, we found that the hours per day they could be out foraging had collapsed. They would barely have been able to emerge to bask before having to retreat.”

Madagascar is a hotspot of extinctions, where 21 percent of local lizard populations have disappeared. Extinctions are affecting species in five lizard families, including chameleons and gekkos. Photo by Ignacio De la Riva.

Sinervo used these findings to develop a model of extinction risk based on maximum air temperatures, the physiologically active body temperature of each species and the hours in which a lizard’s activity would be restricted by temperature.

From climatologists, the researchers were able to get extremely detailed maps of maximum daily air temperatures over the entire planet in the past and present, as well as projections for the future based on climate models. To validate the extinction risk model, the U.S., French, and Mexican teams enlisted the help of colleagues around the world to provide data on local extinctions, working with researchers in Argentina, Brazil, Chile, Peru, South Africa and Australia. Sinervo and Miles also conducted “virtual field expeditions” using Google Scholar and Google Earth.

“What’s alarming is that the extinctions are occurring in biodiversity hot spots such as Mexico, southern Africa and Australia,” Miles said. “We were stunned at the extent to which the lizard populations were blinking out in Mexico, which is among the top three reptile faunas on the planet.”

Climate change is occurring too rapidly for lizards to adapt. “We thought we’d see evolution occurring in response to climate change, but instead we’re seeing extinctions,” Sinervo said. “We’re predicting 40 percent of local populations will go extinct, and that will translate into roughly 20 percent of species going extinct by 2080.”

The climate projections used to model extinction risks assume a continuation of current trends in carbon dioxide emissions from human activities. Many of the extinctions projected for 2080 could be avoided if global efforts to reduce emissions are successful, but the scenario for 2050 is probably inevitable, Sinervo said.

“Policy makers talk about how to mitigate species extinction in the future, but these extinctions are happening now,” Miles added. “This isn’t just a local phenomenon, and these shifts are occurring at a rapid pace.”

Funding for this study included grants from the National Geographic Society, National Science Foundation, UC Mexus, UC Santa Cruz (Committee on Research grant), the French National Center for Scientific Research (CNRS), the Mexican National Council on Science and Technology (CONACYT), the Australian Research Council, and research councils in Argentina (CONICET) and Spain (SMSI).